Need your help and advice: Adding electrical stuff...does this make sense?


Hello to all, and happy holidays!

I have build threads posted in a variety of places, but since this particular item is specific to the outdoors/overlanding plans of the future, I thought I would ask here.

I have a 1990 Daihatsu Rocky. My build thread is here, linked below:

I have swapped out the stock alternator, making a whopping 50 amps, with an Isuzu that makes a scorching 75 amps. I can now, obviously, light the world. I won't embarrass myself to show what I'm currently using for a battery, or hold down, and so on. I am about to install a good battery box so I can relocate it and secure it, and then I will be adding an sPOD system, because I'm petrified about my wiring ability. I will be able to get the lights on after this is done.

My question is about how I want to be able to add a battery box in the rear for trips. I do not want to permanently add a second battery, because I don't think I have the space under the hood for it. But I would like the ability to add the battery when it's time to head out. I simply haven't seen how to handle the wiring for this.

I don't want to reinvent the wheel, and if there's a thread for this somewhere, I would be happy to take a link and run away. I should add that I will be pulling my whole dash to add wiring materials anyway, so placing things like a battery controller shouldn't be an issue. I'd like to pull the dash only once if I can.

Thanks in advance!


Engineer In Residence
There are a few threads discussing home made portable power packs. The trailer guys have some good stuff from tongue/hitch boxes that some use.

What are your needs for this battery? Is it running a fridge? Just powering some lights and phone chargers? Do you need high powered spot lights with the engine off? The more specifics the better.

What is your alternators voltage? This makes a big difference in how well your battery will charge.

What size and weight are you looking at (dimensions please).

What charge sources are you planning on? Solar, alternator, shore power?

How long are the trips this battery will be used on? 1-2-3 days? Multi-week? Some shorter trips can be done with just a full charge at home on shore power.

Wiring is not voodoo thankfully. about 75% of the work is picking the right components (including wire and terminals), and the right tools. The remaining 25% is good install practices and double checking your work.


You have really good comments and questions. Allow me to answer them as best I can.

1. I'll check out the trailer guys. I didn't even think about tongue boxes, and I assume people have those rigged up to charge as they drive. I will look, and ask there, too.

2. This battery would be to power a fridge or any other aux items I would expect to bring. I am happy that it is a tiny SUV so I simply can't pack too much anyway. I believe I will look to use cables to attach an air compressor as I need it, though there is an air locker available. I have other needs that cost money, so an air locker would be an addition for 2020, if that company stays in business. I am thinking about having a CB/radio hooked up to it, too, since I won't need those things if I am not on a trail. I do not expect to need lighting with the engine off at all.

3. Just looked up the voltage. It's a "12V" system, and 75 amps. I don't know if that answers the question. I have not hooked anything up to it to test yet, to verify numbers.

4. Size and weight? I assume battery? Completely flexible. Weight is a non-issue at this point, but anything that is "standard" size would likely be fine.

5. Charge sources for sure would be the alt...and maybe a solar panel added later. For now, alt only,

6. I think 3 days is the longest trip I would go on, limited mainly due to my job.

I agree with your final point. I had to do some very minor wiring to get my little beast legal (new turn signals all around and to get the high beams to work) but this is big-boy stuff. I once destroyed the electrical system of my full-size Blazer and this little guy is essentially unobtanium...so I want to pre-plan to avoid ruining my life. :)


Engineer In Residence
There is a large variance in 12V alternator outputs. Anywhere from 13.3V to over 14.7V. If you are at the low end of the spectrum, you cannot rely on the alternator alone to charge your aux battery. If you are near the high end, you can have good success with alternator only charging. If you have a lower voltage alternator, many can have the voltage regulator swapped or modified for higher voltage. This makes lights brighter, and batteries happier.

You are completely flexible then? If weight and space are not an issue, then the best value for batteries would be a pair of GC2 (6v) batteries from sams club (duracell brand). They provide excellent cycle life for around 200-250$ a pair. They are heavy though, 60+lbs each. They are very robust, and will tolerate serious abuse when other more expensive batteries are garbage. With 100-150AH usable (220AH total) they will run small DC fridges for 2-4 days without issue. a 2x GC2 bank will also produce enough current to start all but the largest engines if required.
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So, now, you've blown my mind and are talking about something that I hadn't considered before.

The little dude I'm putting this/these in might not have the space for both, and due to the weight, I would want to split them, one on either side. Does that rule out the use of something like this?

What is most important is that they start the vehicle and can hold up to the use of a winch when needed, and a fridge when needed. If you're using two 6s, are you wiring them in parallel?

/carlsaganmindblown.gif I could not get to post


New member
You can add either 1 or 2 120ah-200Ah 12v deep cycle batteries with an isolator. The isolator will prevent your starting battery from being drained when using the auxillary battery if the vehicle is off. Vmax AGM batteries are a great choice, they come in a variety 12 or 6 Volt sizes and are safe for indoor use.

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Engineer In Residence
I made a component list as a basis for an electrical system here.
Its a bit higher spec than you would need though.

GC2 sized batteries are available in 12V versions. They do not perform as well overall due to thinner plates with less separation. The 6V versions need to be wired in series for 12V total.

If the batteries are placed on opposite sides of the vehicle, you will need to run a crossover cable/wire from left to right. This needs to be sized for your loads. If you are running a winch, that means approximately 0AWG or larger.

Here is a calculator for wire sizing and fusing. Aim for less than 8% drop for lights and similar non-sensitive loads. For critical loads like chargers, pumps, fridges etc, aim for 3% or less voltage drop (total round trip losses).

The GC2 flooded units are rated around 780CCA, which is generally enough for most gasoline engines up to small V8s. Large diesels may need significantly more when cold.


I feel like that's plenty of amps, luthj. Honestly, the engine is a 1.6 4cyl...so it's not hard to crank.

So, now I worry about having "too much" for the few times I would use a fridge. Or use the winch. Of the two, I expect that the winch would get more use where I live. One reason not to wire two 6s together is that there's simply not that much space under the hood. Let's pretend I through a large AGM under there, of whatever size. The sPOD seems like an elegant solution to wiring a ton of extra stuff, but that will take up space, too, more or less the spot where I could throw a second battery on the passenger side. I worry about the weight, but physical space moreso. This is why I was thinking of a battery box to attach when needed, in the rear. I know I'd need to use serious gauge wire between things...but I thought that would be OK.

None of this means that I'm right, of course. Overall, I'm looking to start gathering parts for a Jan/Feb job here...but I have made no decisions and will continue reading and taking advice. I am going to read luthj's "Framework for Inexpensive..." post right now.


Engineer In Residence
Those are good reasons to select a smaller single battery. 100AH or so units are around 60-70lbs. I would still go with a flooded unit if possible. Better value overall, and you can access the electrolyte with a hydrometer for troubleshooting if needed. There is still the risk of no-start if you have a single battery on board though, so it may be worthwhile to consider various permutations of a starting and dedicated aux system. Making a portable powerpack to toss in the rear has some value. There are portable lithium jump-packs that could be carried for emergencies, and they are tiny. Many double as phone/laptop chargers.

The only detriments to over-sizing your battery are extra weight and space consumed.

If you go with 2 6v units, ideally they should be the same temperature, but I have seen setups with 1 battery under the hood and another at the rear. You need beefy cables, but its not a major issue.

On the other side of the spectrum, if you have some extra cash, and want to go lightweight, a 40AH lithium battery pack could meet your Aux needs easily. Connect it to the alternator with good cables, and you could recharge it in 1-2 hours. of driving, and it would run a smallish fridge for 1-3 days. The nice thing about the lithium batteries is that they don't need a regular 100% full charge to avoid early death (like lead), and they are much smaller, and 1/4 the weight of equivalent lead acid batteries.


Engineer In Residence
I have not done much with banks under 200AH, so I don't have first hand experience with batteries around 40AH. You would need to educate yourself on the options.

A quick google turned up this LI-polymer pack. This would not run a winch etc, but could run a fridge and lights with a fuse block etc.

Another smaller unit. (could parallel).

If you are thinking something small-ish, cheap, and not as light, as lead setup using a battery like this.


And a simple enclosure like in this thread.

Depending on your alternator voltage, you may need a dedicated shore power charger for routine top-ups, or some solar. This type of battery with the right cables could assist in powering your winch in parallel with a starting battery. It may be able to power a small winch on its own, but that is highly dependent on the size and type of winch you are using.

You could ask the mfg what the cranking amp rating is on this battery. Given your engine size, it may work fine for starting duty alongside deep cycling on occasion. That would allow double duty on the occasion you need it. Just add a low voltage cut-out to prevent draining too low to start, or carry a small lithium jump start pack for emergencies.
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Expedition Leader
uther you'll want to take a look at the '$50 dual battery' topic, there is extensive discussion there about what you want to do and a lot of basic diagrams for arranging things several different ways.

I did something similar to what you describe in my Suburban, but made some different choices along the way as I was adding the power mods in support of several other purposes and elected to use two identical batteries for Starter and Aux for redundancy. My chief goal was power conversion and being able to power most things and charge most devices. Rather than a typical solar power / deep cycle / powering a cooler for camping for a few days. But the issues of connections. charging, amperages etc are fundamental / very similar.
Some of the details are in my main build topic, link in my sig, and the topic on the 'power module' itself has some useful stuff near the end -

I also want to have a carrier-mounted winch that I can use from either end of the vehicle, so I went ahead and laid in the much heavier cabling needed to support that right off the bat. It's overkill for what I'm doing with that power module right now, but will be needed later. And it's serving as a sort of bus / backbone, now, with negligible voltage drop. ENough so my rooftop solar is just connected at the rear, inside that power module and is essentially backfeeding my Aux, rather than being connected right at the battery terminals. OR to put it another way, the fat 1/0 cabling effectively makes it the same as doing so.


Just wanted to send this along as I continue a "punch list" for work this winter. This is what I am dealing with as of now, regarding space.

Yes, it does appear that a incredibly useless bungee is holding down the battery. No, that is not the only thing securing the battery overall. But yes, this is the side I want to move things to as I work.



If I might humbly suggest, you might be going about this backwards.

I didn’t see anywhere in this thread where you have listed all of the things you want to run. Have you done that? Do you know how many amps you will draw? LED lights draw relatively little... a radio? A fridge? An air compressor? A winch? Of all those items, the only thing to really think about an Aux battery for is a fridge. An S-POD is a really pricey way to add a few switches. It makes a lot of sense for the vehicles where it fits nicely and custom into the interior trim, otherwise... to each their own.

You might consider figuring out what your running draw is, compare it to your alternator, and wire a relay for your lights with a decent battery and be done.


Besides the vehicle itself, which could get by just fine with the stock 50-amp alt, I upgraded the alt to 75amps. I didn't want to go larger to have any extra pull on the engine, though I also deleted the A/C and its belt-driven fun, so that might have offset it anyway.

I can't answer about an air compressor yet. Yes, I want to have one. However, since I'm not having luck with the different people that make air lockers for my weird vehicle, I can't say that I would have one mounted or connect it to the battery at this point. I don't have to start doing this project tomorrow, so I have time to figure it out.

A winch for sure. I think I'm going to go smaller (4-6k lbs) as my vehicle is smaller, and I can't imagine being able to pull out something much larger anyway. Structurally, I'm ready for a winch, and I plan on putting one on and the wiring that goes with it.

I would like to be able to have a fridge, yes. Since I won't be doing any lengthy trips this summer (2019) I am fine with a good cooler, but I'm also trying to plan for the future.

I'm horrified and scared to wire up my own panel and not destroy something. I've seen good reviews for the sPOD panel and being able to mount it without reinventing the wheel is something I'm fine with.

Your final point is great. I need actual data on what I have right now before I do anything, for sure.